1. Field of the Invention
The present invention relates in general to communication systems and components. More particularly, the present invention is directed to RF filters and multiplexers.
2. Description of the Prior Art and Related Background Information
The desire for smaller, lighter, and higher performing electrical filters and diplexers increases as base station functionalities decrease in size and/or are placed in tower tops such as remote radio-heads, antennas with integrated filters, active antenna arrays, or tower mounted amplifiers for the cellular communication systems. Diplexers are used when two frequency bands are combined (or divided in reverse usage). Traditionally, diplexers are made from a number of techniques such as using two bandpass filters in which each filter may be constructed using a variety of techniques depending on the desired performance and both of these filters are joined to a common junction such that operation of each filter remains independent from the other which is also commonly known as phasing. With one common port, two filters separated in bands of frequencies are called a duplexer or a diplexer, three filters separated by bands of frequencies are called a triplexer, four filters separated by bands of frequencies are called a quadruplexer, and the like. More generally, a plurality of filters sharing a common port is called a multiplexer. In some cases, one or all of the filters may consist of a low pass filter, band stop filter, high pass filter, or band pass filter. Generally, diplexing becomes technically challenging as the bandwidths of diplexed filters get wider. Normally, when two filters are combined to form a diplexer in the frequency range below 3 GHz, the filters employed typically have a 3 MHz to 200 MHz bandwidth.
Accordingly, there is a need to provide wide bandwidth diplexers and multiplexers. Also, it is desirable to provide such wide bandwidth diplexers and multiplexers with minimal increased size and cost.